If 49 litres of a milk solution has 63% milk in it, then how much milk should be added to make the concentration of milk 70% in the solution?

$11\frac{13}{30}$ litres

Ratio of milk and water = (63 : 37) x 3 = 189 : 111

Ratio of milk and water after addition of milk 

⇒ 70 : 30 = (7 : 3) x 37 = 259 : 111

In both cases. the ratio of water remains same

⇒ (189 + 111) = 49 Liters,

⇒ 300 units = 49,

⇒ 1 units = \(\frac{49}{300}\) Liters,

Now, milk added = 259 - 189 = 70 units,

⇒ 70 units = \(\frac{49}{300}\) x 70 = \(\frac{343}{30}\) = $11\frac{13}{30}$ Liters.